The present invention relates to vacuum interrupter electrical contacts and a method of fabrication. A vacuum interrupter is a circuit protection device and comprises a sealed envelope with movable contacts disposed within the envelope for making and breaking electrical continuity. The electrical contact structures enclosed within the envelope must carry very large current efficiently and have a low resistance value when the contacts are in the closed or current-carrying position. When the electrical contacts are separated, some of the contact material is vaporized and the contact materials are selected to minimize erosion of the contacts upon separation or arcing.
A widely used contact material used in vacuum interrupters is described in U.S. Pat. No. 3,818,163, are a chromium matrix contact which is infiltrated with copper. Such chromium-copper contacts provide the low resistive value, and high current-carrying capability desired for such contacts, and also the anti-weld and arcing erosion resistance necessary for long life. High density chromium-copper contact materials and method of fabrication are set forth in U.S. Pat. Nos. 4,032,301 and 4,190,753.
The electrical contacts of the vacuum interrupter are supported within the sealed envelope by a conductive support rod or stem which is typically copper. This copper support rod or stem must be electrically connected to the back surface of the electrical contact during fabrication, and this is typically done by brazing. In fabricating large diameter chromium-copper contacts, it has been found difficult to achieve a uniform porosity in the fabricated contact. Areas of high porosity are typically produced in the central portion, and the back surface of the central portion of the contact must be brazed to the support stem. These areas of high porosity can absorb the braze material into the contact structure creating a poor contact-to-stem braze connection. The electrical contacts of a vacuum interrupter are subjected to significant impact forces upon contact closure and the integrity of the braze between the support stem and the contact is critical in withstanding this impact force.
Other contact materials have been used in vacuum interrupters, and it is common to include a high temperature resistance metal or alloy as one component, and a high conductivity metal as a second component. Such a contact is tungsten or tungsten carbide, as the high temperature resistant component, and copper or silver as the high conductivity component.